High tension spark device



July 4, 1939,. A DORAN 2,164,311

HIGH TENSION SPARK DEVICE Original Filed OCT.. 4, 1932 2 Sheets-Sheet l *ATTORNEY July 4, 1939- .1. A. DoRAN HIGH TENSION SPARK DEVICE 2 sheets-sheet 2 Originall Filed Oct. 4, 1932 INVENTOR v ATTORNEY Patented July 4, i939 IIIGII TENSION SPARK DEVICE James A. Doran, Providence, R. I.

Application october 4, 1932, serial No. 636,154 Renewed March 28, 1938 11 claim. (ci. 12a-169) My presentl invention relates to electrode carrying electrical devices requiring insulation against high voltage, and has' specific reference to improvements in spark plugs 'for internal comv l bustion engines.

Conventional spark plugs have certain disadvantages, such as leakage of gas or oil and cracking of insulators. Leakage-of gas or oil occurs frequently because of the customary manner of l mounting the spark plug insulator, as the cylinder pressures act upwardly against the insulator and tend to unset the insulator from its gasket.

The principal object of my invention is to devise an improved spark plug construction which utilizes the cylinder pressure to force the insulator more firmly on its seat. l

Standard spark plug construction uses screw machine products which are ,relatively expensive to manufacture and assemble. It is a further k object of my invention to utilize screw machine products which are more readily manufactured. and to decreasegthe number of parts required, thus lowering the cost of manufacture and of assembly.

g5 With the above and other objects in view, my

invention consists of a novel arrangement of parts more fully disclosed in the detailed description following, in conjunction with the accom- Danying drawings, and moreparticularly defined i in the claims appended thereto.

In the drawings, Fig.` 1 is a perspective view showing the ase sembled spark plug;

Fig. 2 is a vertical central section through Fig. 1 1;

Fig. 3 is a detail fragmentary section showing a modied form of locking arrangement utilizing a spring lock link; i Fig. 4 is a perspective viewV of the spring lock 40 link; .1

Fig. 5 is a detail fragmentary section showing a further modied form of lock arrangement utilizing interengaging threads; 45 1Ftleg. 6 is a perspective view of a novel electrode D a Fig. '7 is a fragmentary sectional view showing a novel undercut flange construction;

' Fig. 8 is a vertical section through a modiiied 50 spark plug construction with both electrodes insulated from ground;

Fig. 9 is a perspective view of a novel contact insulating shell therefor;

Fig. 10 is a. perspective view of a novel contact shell therefor; and

Fig. 11 is a perspective view of a novel insulator therefor. y

Referring to the drawings, and particularly Figs. 1 and 2 the spark plug metallic shell 2li, preferably made of steel, has an hexagonal sec- 5 tion 2| adapted to receive a wrench, and a threaded end 22v for screwing into the cylinder head, the shell "having a flange 23 above the threaded end for engaging4 the usual gasket to aiIect sealing of the cylinder head. The bore -10 of the shell is. cylindrical at the lower end as indicated at 24, and is tapered at the upper end as indicated at 25, to provide a seat for a correspondingly tapered portion 26 of .the insulator 2l. An annular recess 28 is provided in the up- 15 per portion of the cylindrical bore 24 which coopcrates with a correspondingly annular groove 29 provided in the insulator to receive porcelain cement or the like for rigidly sealing the parts together. 20.

'I'he insulator 21 is preferably made of porcelain, although any other suitable material such as mica, glass,'or the like, may be used. As shown in Fig. 2, the insulator has a tapered tip 33, a central cylindrical section 3| 'inV which the 25 Agroove' 29 is formed,and an uppercylindrical section 32, the insulator having a central vertical bore 33 having its upper portion recessed as at 34 and its lower portion countersunk to receive the electrode locking means hereinafter described. g

Mounted in the central bore 33 of the insulator is an electrode 35 having a ilringpoint 36 and a conical ange23'l which seats in the countersunk end of the'insulator bore, the upper end 35 33 of the electrode being threaded to receive a lock nut 38. The depending portion 40 is roughened or knurled, to seat firmly in the recess 34 and be keyed therein, porcelain cement being preferably inserted between the portion 411v and 40 the recess to sealand bond the lock nut in place. 'I'he terminal binding nut 4I may be made as shown, or may be made in any of the conventional forms.

'The lower end ofthe shell is provided with a 45 depending cylindrical flange 43 spaced from the bore 24 to form a seatingshoulder 44 for receiving an electrode plate 45,.the end of the ange 43 being turned over the electrode plate as indicated in Fig. 2 to lock the same in place. 50 lIhe electrode plate includes a plurality of points or prongs 46, spaced from each other, and forming a central opening through which the electrode point 26 extends.

In assembling the spark plug, the insulator is wellv coated over its portions4 25, 29 and 3| with a suitable high temperature porcelain cement compound, these portions being preferably unglazed to increase the sealing adhesion, and the bore of the shell is similarly coated at the corresponding pointsythe insulator is then inserted into the shell through the lower portion thereof and pressed into position with sumcient pressure to fill the bearing surfaces and the cooperating grooves with the compound, the excess compound being forced out of the shell through the upper end thereof. When the compound is dried and set it seals the insulator to the shell and also forms a solid collar in the cooperating grooves Vwhich bonds the insulator into permanent sealed engagement with the shell, the -cross sectional area of the collar being suicient to provide a liberal factor for safety against shearing in order to ensure against loosening of the insulator by 20 the vacuum pull of the piston or the vibration of the engine. The electrode is then inserted through the insulator, the conical ange and the countersunk seat being coated with sealing compound, and is locked in placeby means of the lock nut, which preferably sets in sealing cement in the ,recess at the head end of the insulator, the electrode plate then being mounted at the lower end of the shell as hereinbefore described.

The improved construction utilizes a minimum number of parts which are of inexpensive manufacture,v and facilitates quick and accurate assembly; the arrangement increases sparking effectiveness and at the same time eliminates leakage of gas'and oil.

Whenever a more positive lock for the insulator is desired, a. construction such as indicated in Fig. 3 preferred. 'I'he insulator 21 is provided with an annular groove 41, andthe shell is provided with a corresponding annular recess 48; a resilient metallic ring 49, see Fig. 4, is snapped into the recess 48, and locks into the groove 41 after the insulator has been forced upwardly into position, cement compoundrbeing used with this construction to provide-a seal. This construction provides a positive lock, as the plastic cement compound flows and lls the space between the` surfaces and the grooves surrounding the ring; when the sealing compound hardens, the ring is imbedded in such position that the insulator is.

positively locked against loosening.

If desired, a construction such as shown in Fig. 5 may be utilized, the insulator 21 being provided With threads 50 which screw-threadedly engage corresponding thread grooves 5| in the shell 20. Sealing cement is first positioned around the thread grooves 5l, and the threading lof the insulator to the shell `forces the sealing compound upwardly so as to iill all spaces between the cooperating threads and between the cooperating tapered surfaces; when the sealing compound hardens the insulator is positively locked to the shell. y

The above described shell construction facilitatesA the formation of spark plug flanges which have a larger diameter than the vhexagonal seetion for receiving the operators wrench. Thus,

referring to Fig. '1, the shell 20 may be` grooved so as to provide a downwardly extending lip rim 52, which is then readily spread with suit# able dies to the position indicated by the dotted lines to provide a sealing gasket flange of greater diameter than the original diameter of the bar stock. The provision of an annular undercut groove thus permits formation of a sealing gasket flange of large diameter from bar stock of smaller diameter, this procedure reducing the cost of manufacture by lowering the material cost and by reducing the cutting time. This method is especially valuable for spark plugs which seat in deep cavities and so require an hexagonal portion 5 of smaller diameter; such plugs have heretofore required formation of the hexagonal portion by milling.

The ground electrode may be of conventional type, but I prefer the construction illustrated `in Fig. 6. A round electrode blank is cut with a punch and die and has a circular rim provided with one or more radial prongs 46 extending towards the center, the arms being spaced from each other to form a central opening of suicient diameter to give the proper gap distance between each arm andthe central electrode. The construction facilitates adjustment of the spark gaps, as'the arms are initially bent as indicated in Fig. 2, and may be bent towards the central electrode to close the gaps or bent away to enlarge the gaps. This spark gap construction greatly prolongs the life of the spark plug and facilitates combustion, as the spark will rst jump against the shortest gap, and then as the metal burns away will jump across another gap. This continues indefinitely, so that the prongs gradually burn away in rotation, and one or two of the gaps will often be free from ring, thus greatly prolonging the life of the spark plug.

' Furthermore, the use of a plurality of electrode arms permits firing even though one or more gaps may be fouled with oil, thus ensuring adequate sparking.

It has been found that spark plugs of the con- 3= ventional type, particularly spark plugs utilized for aeroplane internal combustion engines, comv' monly fail because the insulator cracks. This is due to the standard construction which requires permanent pressure on the central portion of the insulator to keep it sealed on its metalgasket, and which necessitates having the central portion of the body of large diameter with abrupt changes to smaller diameters above and below; moreover, the abrupt changes of temperatures at 45 the necks above and below the central portion produce three zones of temperature with a sharp line of demarcatibn between each zone.

My improved spark plug is practically free from crack failure as the insulator is not subjected to localized constructions or pressures, nor to such sharply divided temperature zones. The ring end of the insulator becomes heated as usual by the burning gases, and the central portion becomes cooled by means of the shell being the same temperature as the adjacent water cooled part of the cylinder; but the peculiar shape of the infsulator produces a gradual transition between these two temperatures and eliminates the tendency to crack. Furthermore, the novel sealing of the insulator in the shell permits free expansion and contraction of the insulator inall directions, so that the insulator is practically free from all risk of cracking.

An ungrounded spark plug construction is shown in Fig. i3, similar to myl novel form of grounded plug, except that an insulating sleeve 66 is provided wh" serves to insulate both electrodes from gro d,and a tubular member 61 is utilized which carries an electrode at its lower end and has a terminal head at its upper end. In the assembly of the ungrounded plug, the shell. 68 is of conventional exterior form, but its bore contains a tapered seat 69 and a cylindrical portion 10 with an annular recess 1I adjacent its upper end. The insulator is made to t the interior of the shell, and is provided with a groove .2 to correspond with the recess in the bore in the shell. When assembling, these bearing surfaces are coated with sealing compound to fill the grooves and to form a collar 'which maintains the insulator in sealed engagement with the shell.

The metal tube 61, l (preferably made from a material-having a low coeiiicient of expansion) is threaded at its upper end, and is of such construction and shape as to t within the insulator. Perforated openings 13 are provided adjacent the tapered portion of the metal tube which assist in maintaining the sealed position of the parts by allowing the sealing compound to form a continuous binding section between the inner insulator 14 and the outer insulator 66, in conjunction with annular grooves 15, 16 in the insulators. The bearing surface between `the outer tapered portion of the tube and the inner tapered portion of the insulator are coated with sealing compound before being pressed together, thus making the assembly an integral unit. The insulator 14 projects above the tube 61 for a suilicient distance to prevent risk of a short circuit between the two terminals; the center portion of the insulator is formed to fit within the tube, and the lower Iend of the insulator is tapered to form the tip which supports the central electrode 15, which is made and mounted as in the novel grounded plugs previously described. A threaded nut 16 is mounted on the threaded end of the tube and is screwed down against the end face of the insulay tor to draw the two into sealed engagement and to permanently maintain them in such position, the nut being provided with an annular groove 11 which serves as a receiving device for the terminal of a lead wire. The lower end of the tube is provided with an annular seat for a, plate electrode of the type previously described, having.a plurality of spaced prongs.

While non-ferrous alloys may be used for te Y electrodes, I prefer to use a ferrous alloy of high tungsten and chromium content, and of a substantially no carbon content, as I :dnd that such alloy has higher heat resistance, is non-corrosive and is non-hardening. Ihese characteristics produce electrodes of exceptionally long life and effectiveness.

While I have described specific spark plug constructions, it is evident that desired changes in construction, in relative arrangement of the parts, in their proportions, and in the materials utilized, may be made to suit the requirements of particular high tension systems, within the spirit and the scope of the invention as defined in the appended claims.

I claim:

1. An insulator'for a spark plug having a cylindrical center portion, a tapered tiring tip portion, and a contact end portion of smaller diameter than said center portion and joined to said center portion by a tapered seat portion, said cylindrical centerportion having an annular groove.

2. In the manufacture of spark plugs, the method of sealing an insulator member in the bore of a shell member comprising forming aligned annular spaces in said members, filling said aligned annular` spaces with sealing compound, and hardening said sealing compound to provide a sealing and locking bond.

3. In a spark plug, an insulator having a bore, said bore being countersunk at the ilring end and recessed at the other end, an electrode extending through said bore, and having a ange seated in 3 said countersink, locking ineaiis lseated in said recess and engaging the other end of said electrode to lock said electrode in said bore, an.`I sealing means in said countersink and recess for sealing the electrode in the insulator.

4. In a spark plug, a shell having one end adapted to be mounted in a cylinder head and having a. bore, said bore having a cylindrical por* tion and a portion tapered towards `the other shell end, and an insulator in said borel having a cylindrical portion engaging the bore cylindrical portion and a tapered portion engaging the bore tapered portion said bore and said insulator having aligned grooves, and sealing means in said aligned groov 5. `In a spark plug, a shell having one end adapted to be mounted in a cylinder head and having a bore, said Lbore having a cylindrical portion and a portion tapered towards the other shell end, and an insulator in said bore having a cylindrical portion engaging the bore cylindrihaving an aligned annular recess, and sealing '7. In a spark plug, a shell threaded at one end for mounting in a cylinder head and having a bore, a seat for an insulator in said bore, an inprovided, and sealing compound in said annular space locking said insulator to said shell.

A3. In a spark plug, a shell threaded at one end for mounting in a cylinder head and having a bore, a seat for an insulator in said bore, an insulator 'in said bore contacting said seat, said insulator having a groove and said shell a corresponding recess, and means in said groove and recess locking said insulator to said shell, said means including an expanslble ring imbedded in sealing compound. A

9. In a spark plug, a shell threaded at one end for mounting in a cylinder head and having a bore, a downwardly facing seat for an insulator in said bore, an insulator in said bore having an upwardly facing surface bearing against saidseat, Said insulator having a portion of smaller diamj eter forming an annular shoulder, and said shell having a corresponding recess aligned therewith and forming an opposed shoulder, whereby an annular space is provided, and sealing compound in said annular space and between said opposed shoulders and locking said insulator to said shell, said sealing compound opposing vacuum in the cylinder, and said bearing seat opposing cylinder pressures and thereby preventing cylinder pressures from affecting the seal.

10. In a spark plug, a shell adapted to be mounteddn a cylinder head and having a bore, a seat' for an insulator in said bore, an insulator in said bore contacting said seat, said shell bore having a threadgroove and saidinsulator having a thread engaable with said thread groove to 'lock said insulator to said shell, said thread and 11. An insulator for a spark plug having a' cylindrical center portion, a.v tapered ring tip portion, and a contact end portion of smaller diameter than said center portion and joined to said center portion by a tapered seat portion, said cylindrical center portion having an annular` groove, said insulator having a bore therethrough, the firing tip end of said bore being 5 countersunk.

l v JAMES A. .DORAN. 

